German researchers have uncovered a six-armed brittle star fossil in the midst of regeneration, a rare discovery made in a southern German limestone quarry that once was a vibrant deep lagoon filled with coral and sponge beds. Today, the site is known for its rich collection of fossils including shark teeth, as well as the remains of ancient pterosaurs, crustaceans, and reptiles dating back to the late Jurassic period.
This fossil represents the first identified instance of a new species named Ophiactis hex. This species exhibits a unique form of reproduction known as fissiparity, where the organism splits in two, and each half regenerates the missing parts, effectively cloning itself. This process, often seen in some modern brittle stars and starfish, usually results in a creature with an even number of arms, typically six, to facilitate an equal division.
The study, published in Proceedings of the Royal Society B: Biological Sciences, notes that while the process of clonal fragmentation is fairly well understood in current biology, its evolutionary and historical aspects remain largely unexplored.
Ophiactis hex fossil reveals clues about early echinoderm fragmentation
The 155-million-year-old Ophiactis hex fossil displays exceptionally well-preserved hook-shaped arm spines, providing significant insight into the ancient origins of clonal fragmentation among echinoderms with star-like forms.
Named after the supercomputer in one of Terry Pratchett’s Discworld novels, this discovery highlights the long-standing nature of fissiparity as a method of asexual reproduction linked to this symmetrical body structure.
The research emphasizes that finding brittle star skeletons with arms in mid-regeneration is relatively common, but fossil evidence showing half-body regeneration is extremely rare. “To the best of our knowledge, the specimen described in the present paper is only the second case known so far, and the first one where regeneration is indeed connected to a six-fold symmetry and clonal fragmentation,” the study states.
Given that only one specimen of Ophiactis hex has been found, determining its exact pre-division appearance and confirming its six-armed structure remains challenging, the researchers noted.